A wireless power transmission technology is employed for various devices or apparatuses for the sake of its convenience to wirelessly transmit electric power using a power transmission coil and a power receiving coil. In such a wireless power transmission technology, there has been a problem that electric power is accidentally fed to metals in the vicinity of the coils. There is known a technique to detect a foreign substance in order to solve the problem. The technique is employed for power transmission equipment having metals in the vicinity thereof and is based on a phenomenon that moving a metal closer to a resonance circuit used in the equipment changes a resonance frequency of the circuit.